Lubrication System and Internal Combustion Engine Comprising Such a System

ABSTRACT

This lubrication system includes a pump feeding a main line which provides oil to a support interface for a crank shaft of oil engine and an auxiliary line connected to at least one piston cooling jet. The pump is a variable flow pump controlled on the basis of oil pressure in the main line. A proportional means is mounted on the auxiliary line. This means is adapted to control oil flow in the auxiliary line depending on the working conditions of the engine, e.g. oil temperature, torque to be delivered or rotational speed of the engine.

BACKGROUND AND SUMMARY

This invention concerns a lubrication system for an internal combustion engine. It also concerns an internal combustion engine including at least such one system.

In order to lubricate moving parts of an internal combustion engine, it is known to use a pump which feeds oil to different locations in the engine. In order to determine the capacity of such a pump, one generally considers a standard working condition of the engine, e.g. the torque point of the engine, that is the working condition of the engine at 1000 rpm. However, depending on the actual rotational speed of the engine on the torque to be delivered, on the temperature of the oil, etc . . . the working conditions of the pump may vary to a great extent. It is therefore known, e.g. from WO-A-2004/065765, to use an oil pump controlled via a pressure-sensing means acted on by the working pressure of the oil. With such a system, one- can bypass the pump under certain circumstances but the pump works at a constant pace, which means that some power is wasted.

It is also known, e.g. from U.S. Pat. No. 5,220,891, to feed some piston cooling jets with oil in order to cool down the pistons and cylinder units of an internal combustion engine. An oil pump sucks lubricating oil stored in a sump and feeds a delivery path where distribution of oil is controlled by throttles. The pump delivers the same quantity of oil, independently of the actual working conditions of the engine.

EP-A-1 362 993 discloses a lubrication system with an electrically driven pump which feeds oil to a crankshaft and to cooling means. The system is complex and, therefore, quite expensive.

The invention aims, according to an aspect thereof, at providing a lubrication system which is adapted to feed oil to a crank shaft and to at least one piston cooling jet, this system needing less power than the ones of the prior art, which means that the overall fuel consumption of an engine equipped with such a system can be lower than the one of engines equipped with systems of the prior art.

The invention concerns, according to an aspect thereof, a lubrication system for an internal combustion engine, this system comprising a pump feeding a main line providing oil to a support interface for a crank shaft of the engine, and an auxiliary line, connected to at least one piston cooling jet, characterized in that:

-   -   the pump is a variable flow pump controlled on the basis of oil         pressure in the main line, and     -   a proportional means is mounted on the auxiliary line, this         proportional means being adapted to control flow of oil in said         auxiliary line depending on the working conditions of the         engine.

Thanks to an aspect of the invention, the work of the pump can be automatically adapted to the flow conditions of oil in the main line, whereas the proportion of oil directed to the piston cooling jets can be controlled by the proportional means on the basis of the working conditions of the engine. This allows an optimization of the working conditions of the pump, which means that the power needed to drive this pump is optimized in all working conditions of the engine.

According to further aspects of the invention, a lubrication system according to the invention might incorporate one or several of the following features:

-   -   The pump is a variable displacement pump. In such a case, it         might be a vane pump, or a sliding gear pump.     -   The pump is a variable timing pump, e.g. a gerotor pump.     -   The pump is a variable speed pump.     -   The lubrication system includes pressure sensing means adapted         to determine oil pressure within the main line downstream of the         pump, this pressure sensing means delivering a signal adapted to         control said pump. The pressure sensing means might include an         oil conduit connecting a portion of said main line located         downstream of said pump to the internal volume of said pump. In         an alternative embodiment, the pressure sensing means delivers         an electrical signal and is connected via an electrical line to         an electronic control unit which pilots the variable flow pump:     -   The proportional means might be piloted on the basis of oil         temperature in the main line, on the basis of the load of the         engine or the torque delivered by the engine, on the basis of         the engine speed, or on the basis of the actuation of an         auxiliary equipment.     -   The proportional means might be a proportional valve or a         piloted flow regulator.

The invention also concerns, according to an aspect thereof, an internal combustion engine comprising at least a crank shaft and at least one piston cooling jet, this engine including also at least a lubrication system as mentioned here above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood on the basis of the following description, which is given in correspondence with the annexed figures and as an illustrative example. In the annexed figures,

FIG. 1 is a scheme of a lubrication system according to a first embodiment of the invention,

FIG. 2 is a schematic cross-section of a vane pump belonging to the system of FIG. 1 , and

FIG. 3 is a scheme similar to FIG. 1 for a lubrication system according to a second embodiment of the invention.

DETAILED DESCRIPTION

The lubrication system represented on FIG. 1 is adapted to be mounted onto an internal combustion engine 1 which comprises a crank shaft 11 and several cylinders 12, only two cylinders being represented. A piston 13 is slidably movable within each cylinder 12, between a top dead center position and a bottom dead center position represented on FIG. 1. A piston cooling jet 15 is provided for each cylinder 12 and is adapted to direct a flow of oil towards its piston 13 in its bottom dead center position, as represented by arrows Ai on FIG. 1.

Crank shaft 11 is supported by several bearings 16. Only one bearing is represented on FIG. 1. Oil is to be fed to each interface between a bearing 16 and crank shaft 11.

To this purpose, a lubrication system 2 includes a vane pump 21 adapted to suck oil from a sump and to feed a heat exchanger 23 which, itself, feeds two lines, namely a first line 24 feeding the interface between crank shaft 11 and at least one bearing 16 and a second line 25 feeding piston cooling jets 15.

A central line 27 runs from pump 21 to a separation point P between lines 24 and 25. Lines 24 and 27 form together the main line for the circulation of oil coming from pump 21 and going towards crank shaft 11 , whereas line 25 is an auxiliary line dedicated to the feeding of jets 15.

An optional safety pressure relief valve 26 is mounted on central line 27, upstream of heat exchanger 23. This pressure relief valve sends oil back to the sump 22 in case pressure within line 27 is higher than a predetermined level.

Oil provided to crank shaft 11 or to piston cooling jets 15 is directed, after use, to sump parts 221 and 222, these parts being connected to the main sump 22.

An oil pressure intake 28 is installed on line 24 and feeds a conduit 281 which opens in the internal volume V21 of pump 21. This provides to pump 21 the value of oil, pressure in line 24, in the form of an analogous signal S-], which is used to move downwardly on FIG. 2 the central rotating body 211 of pump 21, against the action of a spring 212.

Body 211 bears several vanes 213 which are each loaded by a spring 214 to extend radially away from the center C of body 211. Vanes 213 can be pushed towards center C when they interact with the carter 215 of pump 21. The load due to spring 212 can be adjusted by a screw 216.

The translation of body 211 , under the action of the force F exerted by the pressure in line 24 and conduit 281 , changes the displacement or capacity of pump 21.

In other words, the pressure value in line 24 exerts on body 211 a force F which changes the displacement of vane pump 21.

Therefore, the value of oil pressure in line 24 is used to control the flow rate of oil fed by pump 21 to lines 24 and 25, through central line 27.

Other types of variable displacement pumps might be used with the invention, like a sliding gear pump. Moreover, a variable timing pump can also be used, for example a gerotor pump. For these types of pump too, the value of oil pressure can be provided to the pump via a conduit connected to a pressure intake in the main line.

A proportional valve 29 is mounted on auxiliary line 25 and piloted by an electronic control unit 30. Valve 29 creates a variable restriction in line 25 and controls the flow rate of oil provided to assembly 14, separately from the flow rate of oil provided by pump 21 to crank shaft 11.

In the example of FIG. 1, a temperature sensor 31 is mounted on line 27 and delivers an electrical signal S2 to unit 30 via an electrical wire 32. Unit 30 drives valve 29 while taking into account this temperature signal.

Thanks to the invention, the flow rate of oil within main line 24 is automatically adapted by a control of its pressure via intake 28 and conduit 281. On the other hand, the flow rate of oil to the piston cooling jets 15 is controlled, depending on oil temperature, via unit 30 and valve 29. Therefore, the working conditions of variable flow rate pump 21 are adapted to the actual needs in oil. If oil is cold, the power needed to drive pump 21 will be relatively low since the flow rate of oil to be delivered by pump 21 to shaft 11 will be low, to keep an adequate pressure at the interface between the shaft and the associated bearings 16, and jets 15 will be very efficient with a small quantity of oil, so that valve 29 can restrict flow in line 25.

For high engine speeds, e.g. superior to 1300 rpm, pump 21 does not generate a very high flow since its capacity is automatically adapted in order to take into account the actual oil pressure within main line 24.

In all working conditions of the engine, main line 24, which feeds crank shaft 11 is fed at the desired pressure and the flow rate to the piston cooling jets is set by more or less restricting the flow in auxiliary line 25. When valve 29 is fully opened, a maximum oil flow is directed to pistons 13 to cool them. Such a situation arises when engine 1 runs at high speed or delivers a high torque.

When valve 29 is closed, the flow rate needed from pump 21 can be lowered to a flow rate adapted to feed crank shaft 11 only.

Because of the invention, the power consumption of the pump will be much lower than in the prior art systems. In particular, at high engine speed, pump 21 requires about 25% less power than a standard pump of a prior art system. Independently of the engine speed, proportional valve 29 decreases the power needed to drive the pump up to −20% to −30%. One can expect that this will decrease the overall fuel consumption of the vehicle by about 1% under standard conditions like flat motorway.

In the second embodiment of the invention represented on FIG. 3, the same elements as the ones of the first embodiment have the same references. The lubrication system 2 of FIG. 3 includes a variable speed pump 21 which sucks oil from a sump 22 and feeds a central line 27 from which a first line 24 and a second line 25 are fed. A pressure sensor 28 determines oil pressure in central line 27 and delivers, via an electrical wire 282, an electronic signal S-i to control the operation of a variable speed oil pump 21.

Pump 21 is driven by a motor 217 through a rigid shaft 218. Motor 213 is controlled by an electronic control unit 219 to which signal SI is provided.

Depending on the electrical signal Si received from sensor 28 via wire 282, unit 215 might increase or lower the speed of motor 214 and pump 21 , which influences the flow rate of oil in lines 27, 24 and 25.

Oil is fed by pump 21 to an interface, between a crank shaft 11 and at least one bearing 16, and to several piston cooling jets 15, respectively by lines 24 and 25. A proportional valve 29 is installed on line 25 and controlled by an electronic control unit 30. This control unit determines the control strategy for the piston cooling jets flow represented by arrows Al. This strategy may take into consideration the oil temperature in line 28, as measured by a sensor 31 and delivered as an electronic signal S2. It may also take into consideration the engine speed represented by another signal S3, the engine load or the torque delivered by the engine represented by other signals S4 and S5. Other variable parameters can be taken into account at this stage, e.g. parameters depending on the type of oil sucked from pump 22.

The electronic control unit can also pilot valve 29 on the basis of a signal S6 representing the actuation of a compression brake 4 of engine 1. In fact, signal S6 can be representative of the actuation of other auxiliary equipments of engine 1 , like a centrifugal filtration unit.

As for the first embodiment, the use of variable flow pump 21 and proportional valve 29 allows to optimize the power needed to efficiently feed the support interface of crank shaft 11 and jets 15.

According to an embodiment of the invention which is not represented, the proportional valve 29 can be replaced by a piloted flow regulator, that is a mechanical device which controls flow within line 25 with a moving part loaded by a spring or a fluid, the load exerted on this element being adjustable.

Thanks to the invention and as represented on FIG. 3, pressure in main line 24, 27 is unlikely to become too high so that no pressure relief valve similar to the one of the first embodiment is really necessary in both embodiments.

The individual features of the above mentioned embodiments can be combined. In particular, unit 30 of the first embodiment can control valve 29 on the basis of all the parameters mentioned with respect to unit 30 of the second embodiment.

LIST OF REFERENCES

-   1 engine -   11 crank shaft -   12 cylinder -   13 piston -   15 piston cooling jet -   16 bearing lubrication system -   21 variable displacement pump -   211 central body -   212 spring -   213 vanes -   214 springs -   215 carter -   216 screw -   217 motor -   218 shaft -   219 electronic control unit -   22 sump -   221 sump part -   222 sump part -   23 heat exchanger -   24 main line -   25 auxiliary line -   26 pressure relief valve -   27 central line -   28 oil pressure intake/oil sensor -   281 conduit -   282 electrical wire -   29 proportional valve -   30 electronic control unit -   31 temperature sensor -   32 electrical wire -   4 compression brake -   Ai arrows -   C center of body 211 -   F force exerted by oil pressure on body 21 1 -   P separation point -   S1 signal (oil pressure) -   S2 signal (temperature) -   S3 signal (engine speed) -   S4 signal (engine load) -   S5 signal (engine torque) -   S6 signal (actuation of 4) -   V21 internal volume of pump 21 

1. A lubrication system for an internal combustion engine, the system comprising a pump feeding a main line, providing oil to a support interface for a crank shaft of the engine, and an auxiliary line, connected to at least one piston cooling jet, wherein: the pump is a variable flow pump controlled based on oil pressure in the main line, proportional means is mounted on the auxiliary line, the proportional means being adapted to control oil flow in the auxiliary line depending on working conditions of the engine, and the system includes pressure sensing means adapted to determine oil pressure within the main line downstream of the pump, the pressure sensing means delivering a signal adapted to control the pump.
 2. A lubrication system according to claim 1, wherein the pump is a variable displacement pump.
 3. A lubrication system according to claim 1, wherein the variable flow pump is a vane pump.
 4. A lubrication system according to claim 1, herein the variable flow pump is a sliding gear pump.
 5. A lubrication system according to claim 1, wherein the variable flow pump is a variable timing pump.
 6. A lubrication system according to claim 1, wherein the pump is a variable speed pump.
 7. A lubrication system according to claim 1, wherein the proportional means is piloted based on oil temperature in the main line.
 8. A lubrication system according to claim 1, wherein the proportional means is piloted based on engine speed.
 9. A lubrication system according to claim 1, wherein the proportional means is piloted based on load of the engine.
 10. A lubrication system according to claim 1, wherein the proportional means is piloted based on actuation of auxiliary equipment.
 11. A lubrication system according to claim 1, wherein the proportional means is a proportional valve.
 12. A lubrication system according to claim 1 wherein the proportional means is a piloted flow regulator.
 13. An internal combustion engine comprising at least a crank shaft and at least a piston cooling jet, comprising at least a lubrication system according to claim
 1. 14. A lubrication system according to claim 1, wherein the variable flow pump is a gerotor pump.
 15. A lubrication system according to claim 1, wherein the proportional means is piloted based on torque delivered by the engine. 